1. Field of the Invention
The present invention relates to a recording device having one of several ranks of print heads, the print head requiring application of a specific drive voltage depending on its rank.
2. Description of the Related Art
There has been known an ink jet recording device for printing in a plurality of colors. The ink jet recording device has an ink jet head unit having: a black head for ejecting black ink, a yellow head for ejecting yellow ink, a cyan head for ejecting cyan ink, and a magenta head for ejecting magenta ink. Each of the heads is formed with a plurality of ink chambers and nozzles, wherein the ink chambers are connected to corresponding nozzles. One piezoelectric element is provided in each ink chamber. Applying a voltage to any of the piezoelectric elements will cause the piezoelectric element to deform so that the volume of the corresponding ink chamber changes. By selectively changing the volume of ink chambers ink this manner, pressure can be applied to the ink in the ink chamber so that ink droplets are ejected from the corresponding nozzles to print images on a printing medium.
In order to ensure stable print quality, it is necessary that ink droplets are ejected from nozzles of all the heads at the same ejection speed and so as to have the same volume. However, the different heads are produced on different production lines so that variation results in different production lots. Therefore, even if the same voltage is applied to piezoelectric elements in the different heads, there will be variation in the volume in the ejected ink droplets and in the speed at which the ink droplets are ejected.
FIG. 1 (A) shows drive voltages determined as necessary, under the ejection conditions of room temperature of 25.degree. C. for different ranked heads to eject ink droplets at a fixed speed of five meters per second in this example. Heads requiring application of less than 16 volts or of 23 or more volts are considered unsatisfactory (NG). Heads requiring application of between 16 or more volts and less than 18 volts are placed in a rank A. Heads requiring application of between 18 or more volts and less than 20 volts are placed in a rank B. Heads requiring application of between 20 or more volts and less than 23 volts are placed in a rank C. FIG. 1 (B) shows the drive voltages required to drive heads of the different ranks under nine different temperature ranges, set by dividing the temperature range of 0.degree. C. to 50.degree. C. is divided into nine temperature ranges.
Each head of each color is ranked in the above-described manner. Different color heads of the same rank are combined together to produce a single ink jet head unit for printing in full color. However, because the three ranks A, B, and C of ink jet head units each require application of a different strength voltage, when assembling the ink jet recording device, it is necessary to set the ink jet recording device so that it applies the drive voltage, that is, from the three different strength drive voltages, appropriate for the ink jet head unit mounted therein.
A conventional circuit for selecting the appropriate drive voltage is shown in FIGS. 2 and 3. FIG. 2 is a circuit diagram of the circuit for selecting the drive voltage. FIG. 3 is a block diagram of the control system in an ink jet recording device provided with the circuit shown in FIG. 2.
As shown in FIG. 2, in the conventional circuit for selecting drive voltage, a signal line 116 connecting a ground (0V) and a central process unit (CPU) 150 is divided into two signal lines 122, 124. A cut unit 110 is disposed on a chip mounting board (not shown in FIG. 2) and includes a cut portion 112 for cutting the signal line 122 and a cut portion 114 for cutting the signal line 124. A resistor unit 120 is disposed on the chip mounting board (not shown in FIG. 2) and includes a resistor R4 connected to the signal line 122 and a resistor R5 connected to the signal line 124. The signal lines 122 and 124 are connected to output their signals to separate predetermined ports of the CPU 150.
When assembling the driver IC chip 160 into the ink jet recording device, the cut portions 112 and 114 are cut in a manner depending on the rank of the print head, that is, depending on the required drive voltage to be set. Three possible cut patterns are possible, that is, when one or the other of the cut portions 112 and 114 are cut and when neither are cut. According to the cut pattern, one of three digital signals 01, 10, or 00 is outputted across the signal lines 122, 124 to the CPU 150. After determining the type of digital signal, the CPU 150 retrieves a drive voltage corresponding to the determined digital signal from a table stored in a RAM, for example, of the recording device.